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Posted by: Bjorn Jonsson Feb 27 2008, 11:50 PM

After extensive software improvements to speed things up I just finished doing an experimental Iapetus animation based on a new and bigger version of the DEM described in http://www.unmannedspaceflight.com/index.php?showtopic=4546. The new version looks like this:

The animation can be downloaded from http://www.mmedia.is/bjj/misc/css_stuff/anim/iapetus_dem_800x600.avi (almost 5 MB). It requires the DivX codec (see http://www.divx.com )

A sample frame from the animation:


The animation starts and ends 3000 km from Iapetus' center and gets to within about 300 km from the surface. Vertical relief is exaggerated by a factor of 3. I may do a new version later with the horizon horizontal at close range and not vertical as in this animation. Flying over a bigger part of the surface at close range is another idea.

The texture map was generated as a byproduct when doing the DEM so it fits the DEM perfectly. It was processed to make dark terrain lighter, otherwise the animation appears too dark.

Once I have a DEM covering a bigger part of Iapetus I will update the animation.

Posted by: djellison Feb 28 2008, 12:05 AM

****ing hell that's good. This community is lucky to have code monkeys like you

Posted by: nprev Feb 28 2008, 01:29 AM

Uh....WOW?!?!?!?!!!

I was gonna try to inject a creative curse, but words honestly fail me. Thanks so much for this, Bjorn!

Posted by: tedstryk Feb 28 2008, 01:42 AM

Wow, that is amazing! It looks very real - not the cartoonish feel that such things have when based on poor quality DEMs.

Posted by: mchan Feb 28 2008, 05:26 AM

Ditto Wow!

Posted by: djellison Feb 28 2008, 08:14 AM

Ahh - so you HAVE seen the HRSC stuff then.


Doug

Posted by: ugordan Feb 28 2008, 08:38 AM

This has got to be one of the coolest animations that came out of Cassini, ever. It's the next best thing to actually having a shape model of Iapetus on your desk!

Outstanding work, Bjorn!

Me wants a global DEM at that resolution... *droool*

Posted by: ngunn Feb 28 2008, 11:47 AM

I'd love to see this (even with 3x vertical exaggeration) but unfortunately it won't play on our system.

As a matter of curiosity how do you define vertical exaggeration on a non-spherical body?

Posted by: Ian R Feb 28 2008, 11:57 AM

Bjorn, you're going to have to put this animation on YouTube - it's simply awesome!

Posted by: ugordan Feb 28 2008, 11:57 AM

Nigel: You can calculate normals to each point of the surface and exaggerate along that direction, which works fine even for triaxial ellipsoid approximations.

Posted by: ngunn Feb 28 2008, 12:19 PM

Yes, but those normals won't be truly vertical in a gravitational sense. I'm sure the difference is reasonably small for Iapetus, but it might be considerable when we get to somewhere like Vesta. If you wanted to compare local slopes with the angle of repose (for example) you'd have to be careful with this. Of course you could avoid the issue completely by doing no exaggeration.

Anyhow, I'd better leave this thread to those of you fortunate enough to be able to view the animation.

Posted by: ugordan Feb 28 2008, 12:36 PM

If it's gravitational-sense-vertical you're worried about, you can compute the center point of the body (center of the ellipsoid) and use the surface radius vector instead of surface normal vector for exaggeration. That should be damn close to gravitational vertical.
I wonder which method Bjorn actually uses. From a rendering point the surface normal method appears to be more straightforward.

Posted by: Bjorn Jonsson Feb 28 2008, 01:45 PM

The vertical exaggeration is very simple. The DEM is normally stored as lat,lon,distance from Iapetus' center. It's also possible to output it as lat,lon,deviation from a triaxial ellipsoid. I simply multiply this deviation by a factor of 3.

This is exactly what I want - for each and every icy Saturnian satellite. I'm hoping to get at least 50% coverage for Iapetus once the September 2007 flyby images hit the PDS. It must be possible to get much more than 50% coverage for Tethys, Dione and Rhea. Mimas is rather poorly imaged relative to the other satellites (especially near and east of Herschel) but that should improve greatly with the 9500 km flyby in 2010. Enceladus is more difficult because of its smoothness.

A DEM for every satellite is a huge project. I've been wondering about possible 'collaborative DEMs' recently. In particular, measuring control points is a lot of work. The process could probably be partially automated but doing so is a lot of work too.